This application claims priority to U.S. Provisional Patent Application Ser. No. 61/481,216, which was filed May 1, 2011. This priority application is hereby incorporated by reference in its entirety into the present application, to the extent that it is not inconsistent with the present application.
In oilfield applications, for example, in deep-sea locations, heavy tubulars extend downward from the platform and may be supported by engagement with a landing string. Depending on the particular application (i.e., drilling, completion, etc.), the landing string may be provided by drill pipe or other high-tensile tubulars. Such landing strings are often required to support a heavy load, such that traditional running systems, which generally employ slips or bushings to hold the tubular by engaging the outer diameter thereof, are inadequate. Further, as offshore drilling operations continually push into deeper water, the tensile load transmission from the landing string to the rig continues to increase in order to support the increased string weight, which is increasingly causing “slip crushing,” whereby the slips and/or bushings engage the tubular body with such force that the tubular body is crushed or otherwise damaged.
To avoid this, landing strings are typically lowered by engagement with an upset (i.e., a shoulder) on the tubular body of the landing string. One way to do this is to employ dual-upset tubulars, allowing the tubular to be lowered by engaging one upset with the elevator and the second with the spider. Another common method shuttles or circulates a pair of elevators to ensure that only the upset is engaged, thereby obviating the need for special dual-upset tubulars. The first elevator begins suspended by the bails, while the second elevator acts as a spider, resting on the rotary table and supporting the landing string by the upset of the upper-most tubular of the landing string (i.e., the most recently run-in segment). The first elevator engages a new tubular segment, positions it with the top drive, and the top drive makes it up to the exposed box of the landing string. The slips or bushings of the second elevator are then disengaged from the upset and the second elevator is removed; thus, the weight of the landing string is transmitted through the new tubular segment to the first elevator. The first elevator then lowers until it abuts the rotary table, and, as such, now acts as a spider. The bails are then switched to the second elevator, which engages another new tubular segment, and the process is repeated.
Such known processes have significant drawbacks, requiring special dual-upset tubulars or time-consuming switching of bails between elevators. What is needed are faster, more cost-effective methods and apparatus for lowering such heavy tubulars, while avoiding slip crushing.